Metal-casting method and apparatus, casting system and cast-forging system

ABSTRACT

[Purpose] To provide, in relation to casting of materials to be subjected to plastic working such as cold forging, hot forging, enclosed forging, rolling, extrusion, and roll-forming of metals, including nonferrous metals, such as aluminum and magnesium (inclusive of respective alloys), and ferrous metals (i.e., iron and steel) or to direct casting of products (i.e., castings), a metal casting method which is capable of yielding cast ingots of healthy interior metallographic structure with no cut surfaces, by making the solidification interface smooth so as to prevent generation of cracks in cast ingots which are otherwise unavoidable due to concentration of solidification shrinkage stress caused by the solidification interface becoming locally concave when the solidification interface arrives at the top surface of the mold to ultimately complete solidification, or by effecting local control of removal of heat from the mold so as to prevent generation of casting defects such as cavities and microshrinkages which are otherwise unavoidable due to the solidification interface of the molten metal in the mold forming a closed surface inside the cast ingot; a casting apparatus; and cast ingots.  
     [Means for Solution] In a method for casting metal by charging molten metal  6  into a closed-space-definable mold  2  which includes a cooling member  1  and in which an end surface of an open/close plug  5  serves as a portion of an inner wall of the mold  2,  removal of heat from a mold member  2  comprising the cooling member 1 is locally controlled in accordance with the shape of cast ingot and the location and number of the molten metal inlet(s)  4,  to thereby solidify the molten metal in such a manner that the solidification interface  6   b  advances to arrive at an end of an inner surface of the mold  2.

TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS

[0001] The present invention relates to casting of materials to besubjected to plastic working such as cold forging, hot forming ofmetals, including nonferrous metals, such as aluminum and magnesium(inclusive of respective alloys), and ferrous metals (i.e., iron andsteel), or to direct casting of products (i.e., castings). Moreparticularly, the present invention relates to a metal casting methodwhich is capable of yielding cast ingots of healthy interiormetallographic structure with no cut surfaces, by making thesolidification interface smooth so as to prevent generation of cracks incast ingots which are otherwise unavoidable due to concentration ofsolidification shrinkage stress caused by the solidification interfacebecoming locally concave when the solidification interface arrives atthe top surface of the mold to ultimately complete solidification, or byeffecting local control of removal of heat from the mold so as toprevent generation of casting defects such as cavities andmicroshrinkages which are otherwise unavoidable due to thesolidification interface of the molten metal in the mold forming aclosed surface inside the cast ingot. The present invention also relatesto a casting apparatus and to cast ingots.

BACKGROUND ART

[0002] In conventional metal mold casting, die casting, and low pressureor high pressure casting, molten metal is teemed into a castingapparatus to form a cast body, after which the sprue portion and feederportion are cut off to thereby provide a stock material. Theseconventional methods require simple steps, and thus have an advantage oflow production cost. However, they are not free from producing castingdefects inside the cast bodies, including cavities, pin holes, shrinkagecavities, and engulfment of oxides.

[0003] As contrasted to such conventional methods, casting by way ofunidirectional solidification provides excellent cast bodies in terms ofquality regarding interior metallographic structure. However, if themolten metal has a free surface which is open to air, the meniscusportion that contacts side walls of the mold forms a curved surfacehaving a large area, thus making it impossible to form a cast bodyhaving a top surface orthogonal to the circumferential side walls.Moreover, since controlling to a constant level the volume of moltenmetal to be teemed is difficult, various disadvantages result, includingsignificant variation in weight of the as-produced stock material,halting of the forging machine due to overload imposed during forging,and significant dimensional variation in the resultant forged products.

[0004] In view of the foregoing, the present inventors have previouslydisclosed in Japanese Patent Application Laid-Open (kokai) No. 8-155627a casting method and apparatus capable of solving the aforementionedproblems inherent to the technique of unidirectional solidification.

[0005] Briefly, as shown in FIG. 15, a mold 2 is disposed on a coolingmember 1, and molten metal 6 is introduced, from a molten metalreservoir 3 provided at an upper section of the mold 2 and via a moltenmetal inlet 4, into the inside of the mold 2 so as not to leave anyspace therein, and subsequently, the cooling member 1 is cooled with theinside of the mold 2 being isolated by means of closing the molten metalinlet 4 with an open/close plug 5, to thereby cause the molten metal 6to solidify unidirectionally. In FIG. 15, reference numeral 7 denotesmolten metal contained in the molten metal reservoir, reference numeral8 denotes a spray nozzle, reference numeral 23 denotes an electricfurnace for maintaining the molten metal at a predetermined temperatureand for preventing cooling, from the side walls of the mold, of themolten metal poured into the mold, reference numeral 24 denotes an upperlid, reference numeral 25 denotes a casing, and reference numeral 26denotes a discharge port for a cooling medium.

[0006] By the employment of the above-described method and apparatus,teeming of a precise, predetermined amount of molten metal 6 into themold 2 can be performed quite easily without need for measurement of themolten metal. Moreover, serial operations, including teeming, coolingfor solidification, and removing the cast product, can be performedcontinuously. In addition, since the molten metal is charged in theclosed mold 2 without leaving any space therein, the resultant castproduct has an outer surface conforming to the inner surface of themold, thereby achieving high dimensional accuracy in thickness andshape. Also, the cast product has excellent quality in terms of internalmetallographic structure, exhibiting no mold cavities, shrinkagecavities, pinholes, engulfment of oxides, or similar defects.

[0007] [Problems to be Solved by the Invention]

[0008] However, the aforementioned method and/or apparatus involves thefollowing problem. That is, particularly when the cast body to beproduced is a thin product having an axisymmetric disk shape of largeouter diameter, time required for solidification of the molten metal atthe molten metal inlet portion—which is located virtually at a centralportion of the disk—is different from that at a peripheral portion ofthe disk which is the remotest from the molten metal inlet portion, andtherefore, an ideal unidirectional solidification state cannot bemaintained, causing a local depression of the solidification interfaceat a location directly below the molten metal inlet and in some casesproducing cracks at a central portion of the cast ingot.

[0009] Under the above circumstances, the present inventors havecontinued further studies in an attempt to obtain cast ingots havingmore healthy internal metallographic structure, and have found thatcontrol of heat removal which is performed locally in accordance withthe shape of the cast ingot to be produced; in other words, furnishingof a control mechanism that realizes a heat removal profilecorresponding to the shape of the cast ingot to be produced, cancontribute to attainment of a flat solidification interface and yieldcast ingots which have no cut surfaces and have healthy interiormetallographic structure. The present invention has been made on thebasis of the above findings.

[0010] [Means for Solving the Invention]

[0011] The present invention, which has been made in view of theforegoing, is accordingly directed to a method for casting metal bycharging molten metal into a closed-space-definable mold which includesa cooling member and in which an end surface of an open/close plugserves as a portion of an inner wall of the mold, characterized in thatremoval of heat from a mold member comprising the cooling member islocally controlled in accordance with the shape of cast ingot and thelocation and number of the molten metal inlet(s), to thereby solidifythe molten metal in such a manner that the solidification interfaceadvances to arrive at an end of an inner surface of the mold (claim 1);a metal casting apparatus for casting metal by charging molten metalinto a closed-space-definable mold which includes a cooling member andin which an end surface of an open/close plug serves as a portion of aninner wall of the mold, characterized by comprising a cooling capacitycontrol mechanism which imparts, to the mold member comprising thecooling member, a heat removal profile appropriate for the shape of thecast ingot to be produced and for the number and position of the moltenmetal inlet(s) (claim 3); and a cast ingot obtained by use of the methodor apparatus (claim 24).

[0012] The above-mentioned prior art Japanese Patent ApplicationLaid-Open (kokai) No. 8-155627 discloses the following methods for theforced cooling of a cooling member.

[0013] (1) Jetting, in the form of spray or shower, a medium onto thelower surface of the cooling member (to effect collision).

[0014] (2) Passing cooling water through cooling water piping providedin the cooling member.

[0015] (3) Installing a cooling water tank at a lower section of thecooling member for passing water therethrough.

[0016] However, any of these modes attains virtually uniform cooling ofa cooling member. Also, the cast ingots to be produced are of simpledisk shape, and this publication does not contain any specificdisclosure for the case of cast ingots of three-dimensionallycomplicated shape.

[0017] As a result of continued energetic research, the presentinventors have found that local control—in accordance with the shape ofcast ingot, the location and number of molten metal inlet(s), etc.—ofheat removal through augmenting or reducing the cooling capacity of themold member having a cooling member or through intentional heating,whereby the molten metal is solidified in such a manner that thesolidification interface advances to arrive at an end surface of themold, eliminates the risk of a closed loop of solidification frontsurface being formed inside the mold and enables provision of a castingot having a healthy interior metallographic structure.

[0018] [Modes for Carrying Out the Invention]

[0019] The cooling capacity control mechanism employed in the method andapparatus of the present invention will next be described in more detailwith reference to the drawings. Methods for forced cooling of a moldmember having a cooling member are basically divided into two types: amethod corresponding to the combination of the aforementioned methods(1) and (3); i.e., a method in which a cooling medium is brought intocontact with an outer surface of a mold member having a cooling member,to thereby cool the cooling member; and a method corresponding to theaforementioned method (2); i.e., passing a cooling medium through thepiping provided in a mold member having a cooling member. Either method,when combined with one of the following modes, establishes a coolingcapacity control mechanism.

[0020] Although the following description mainly focuses on a coolingmember, heat removal from not only the cooling member but from a moldmember having a cooling member is locally controlled by the presentinvention.

[0021] 1. Mode in Which Cooling is Performed by Contacting a CoolingMedium with an Outer Surface of a Cooling Member (Claim 4);

[0022] Specifically, there are the following two types of methods: amethod in which a cooling medium jetted in spray form or shower formhits against an outer surface of a cooling member; and a method in whicha cooling bath to which a cooling medium is supplied is provided outsidea cooling member. However, since local control of heat removal isdifficult to attain when these methods (i.e., forced cooling methods)are used alone, one or more of the following modes “a” to “f” arecombined with one of these two methods, to thereby establish a coolingcapacity control mechanism that locally controls heat removal. In theaccompanying drawings, only apparatuses applicable for top teeming(i.e., molten metal is poured from above the apparatus) are shown.However, the pouring direction of molten metal is not limited thereto,and bottom teeming may also be employed.

[0023] a. Mode Employing a Cooling Member in Which the Wall Thickness ofa Certain Portion is Different from that of Other Portions (Claim 5);

[0024] The molten metal present at the location directly below themolten metal inlet is a lastly teemed portion, and accordingly, thisportion of molten metal will be cooled and solidifies last. Therefore,the corresponding portion of a cast ingot directly below the moltenmetal inlet is prone to microshrinkage, or cracks caused bysolidification stress due to temperature difference in the cast ingot.In order to cope with this problem, the cooling member is partiallythickened or thinned, and a cooling medium is brought into contact withan outer surface of the cooling member, to thereby provide anappropriate profile of heat removal in accordance with the shape of castingot and the location and number of the molten metal inlet(s). Thus,formation of a local depression at the solidification interface can beprevented. Specifically, for example, when the cast ingot to be producedis of a simple disk shape, a portion of the cooling member whichcorresponds to the central portion of the ingot; i.e., the region wheresolidification of molten metal delays, is thinned to thereby enhance thecooling capacity; and a portion of the cooling member which correspondsto a peripheral portion of the cast ingot; i.e., the region wheresolidification of molten metal proceeds quickly, is thickened to therebylower the cooling capacity. Moreover, in connection with the mechanismfor supplying the cooling medium, the amount of the cooling medium to bejetted and the timings to initiate and terminate the cooling process maybe determined in accordance with the shape of the cast ingot. Forexample, cooling may be started either after ultimate completion (thefilled-up state) of teeming of molten metal, or before completion.

[0025]FIG. 1 is a cross-sectional view showing an exemplary apparatus ofthe present invention and depicting a cooling capacity control mechanismof mode “a.”

[0026] In the embodiment shown in FIG. 1, a mold 2 (an upper mold 2 aand a side mold 2 b) is disposed on a cooling member 1. A reservoir 3for receiving molten metal 7 from a melting furnace (not shown) or asimilar apparatus is provided in the upper section of the mold 2, and isheated by means of an unillustrated electric furnace so as to maintainthe molten metal at a predetermined temperature. The reservoir 3 is incommunication with the interior space of the mold 2 (reference numerals6 a, 6 b, and 6 c represent solidified molten metal, solidificationinterface, and unsolidified molten metal, respectively) via a moltenmetal inlet 4. The molten metal inlet 4 is equipped with an open/closeplug 5. Teeming of molten metal into the mold 2 is performed byelevating the open/close plug 5 by means of an open/close plug elevatingmeans (not shown), and when the mold 2 is completely filled up withmolten metal 6 without leaving any space therein, the open/close plug 5is lowered, to thereby block the molten metal to be teemed.

[0027] The thickness of the cooling member 1 is smaller at the centerportion, in which solidification of molten metal 6 delays, and thethickness gradually increases toward the periphery, where solidificationrate of molten metal 6 is high. A spray nozzle 8 disposed below thecenter of the cooling member 1 jets a cooling medium such as water,supercooled water of 0° C. or lower (e.g., supercooled water of 0° C. orlower containing 0.5% or more sodium chloride, or supercooled water of0° C. or lower containing a substance such as ethylene glycol), avolatile liquid such as ethyl alcohol, or an oil so that the coolingmedium hits (or contacts) the lower surface of the cooling member 1, tothereby cool the cooling member 1.

[0028] Structures other than the above-described one may beappropriately selected and determined in accordance with needs asdescribed, for example, in the aforementioned Japanese PatentApplication Laid-Open (kokai) No. 8-155627. For example, when moltenmetal 7 (cast ingot) is Al, Mg, Zn, or an alloy thereof, the coolingmember 1 is preferably made of Cu, Al, or any other metallic materialendowed with excellent refractory property and mechanical strength,whereas when molten metal 7 (cast ingot) is Fe, Cu, or an alloy thereof,the cooling member 1 is preferably made of a ceramic material endowedwith excellent refractory property such as graphite, SiC, Si₃N₄, orBN-containing Si₃N₄. Examples of the material that constitutes the mold2 include a heat-insulating refractory material composed predominantlyof an ordinary refractory material, CaO, SiO₂, Al₂O₃, or MgO, amongother materials; a single substance of SiC, Si₃N₄, black lead, BN, TiO₂,ZrO₂, or AlN, or a refractory mixture thereof; and metals such as Fe andCu. Of these materials, the material to be employed may be selected ingeneral consideration of the metal or alloy to be subjected to casting,temperature at use, wettability with molten metal, corrosion resistance,etc.

[0029] In order to supply the molten metal throughout the interior spaceof the mold without leaving any space, the molten metal 6 in the mold ispreferably pressurized. In the apparatus shown in FIG. 1, pressurizationis effected by the riser effect of the molten metal 7 in the reservoir3. In this connection, the top surface of the molten metal 7 in thereservoir 3 is preferably 30 mm or more above the top surface of themolten metal 6 which fills the mold 2. When such a height difference isprovided, oxides floating on the molten metal 7 contained in thereservoir 3 is prevented from entering the mold 2. Cooling of the moltenmetal 6 must be attained mainly by means of the cooling member 1, andcooling effected through side walls, etc. should be prevented. Thisallows the molten metal 6 to be solidified unidirectionally from thebottom toward above. Upon pouring the molten metal into the mold 2, thecooling member 1 preferably assume a temperature of at least 100° C.When teeming is performed at a lower temperature, disadvantageously, thephenomenon called “blow,” a type of defect typically found in metal moldcasting, is caused. From the viewpoints of cooling efficiency andproduct quality, the upper limit would be approximately the temperatureof molten metal. In order to prevent generation of blows, a mold releaseagent, which is widely used for the application to cooling member 1, isalso effective.

[0030] b. Mode in Which an Interior Space is Provided in a Portion of aCooling Member (Claim 6);

[0031] In the above-described mode “a,” the cooling member is partiallythickened or thinned. Alternatively, when an interior space is providedin a part of a cooling member, thermal conductivity in the thicknessdirection can be varied even in the case in which, for example, theouter thickness of the cooling member is uniform, whereby coolingcapacity control similar to that mentioned above can be attained.Moreover, the interior space prevents heat from flowing from moltenmetal to the outer surface of the cooling member, well-balanced coolingcapacity can be attained throughout the cooling member, contributing toformation of a solidification interface of desired shape.

[0032] Although the interior space is essentially a closed space, it maybe an open space unless it allows a cooling medium to enter thereindeeply. Since the thermal conductivity of the interior space region islower than that of the cooling member, which is generally formed of amaterial of high thermal conductivity, there can be attained a coolingcapacity control similar to that through mode “a,” in which the coolingmember is partially thickened or thinned. Moreover, the interior spaceprevents heat from flowing from the molten metal to the outer surface ofthe cooling member.

[0033] An example of mode “b” is shown in FIG. 8, and a detaileddescription therefor will be given herein later.

[0034] c. Mode in Which the Cooling Member is Made of a CompositeMaterial of Different Thermal Conductivites (Claim 7);

[0035] In the above-described mode “a,” the cooling member is partiallythickened or thinned. Alternatively, when a material segment having athermal conductivity different from that of the remaining portion of thecooling member is integrally formed within the cooling member (FIG.9(a)), or when a material segment having a thermal conductivitydifferent from that of the remaining portion of the cooling member isintegrally inserted into a portion of an outer surface of the coolingmember (FIG. 9(b)), even when the outer thickness of the cooling memberis uniform, the heat capacity in the thickness direction can be varied,attaining a function similar to the aforementioned one. Moreover, thematerial segment having a different thermal conductivity prevents heatfrom flowing from the molten metal to the outer surface of the coolingmember, well-balanced cooling capacity can be attained throughout thecooling member, contributing to formation of a solidification interfaceof desired shape.

[0036] In this case, the cooling member preferably comprises a metallicmaterial and a refractory heat-insulating material, which serves as thematerial segment having a different thermal conductivity, which isintegrally formed inside or outside of the part made of metallicmaterial. Examples of suitable metallic materials include aluminum,copper, iron, and an alloy thereof having a high thermal conductivity.Examples of suitable refractory heat-insulating materials incorporatedinto the inside of the part include a material in the form of plate,blanket, or sheet made of alumina fiber or fused silica fiber; or asingle substance of Si₃N₄, SiC, BN, or graphite, or a mixture thereof.Examples of suitable refractory heat-insulating materials inserted fromthe outside of the part made of metallic material include a singlesubstance of Si₃N₄, SiC, BN, or graphite, or a mixture thereof.

[0037] An embodiment of mode “c” is shown in FIG. 9, and a detaileddescription therefor will be given herein later.

[0038] d. Mode in Which an Outer Surface of the Cooling Member isPartially Provided with an Uneven Surface so that the Area that canContact a Cooling Medium Locally Varies (Claim 9);

[0039] When a cast ingot to be produced does not have a simple diskshape but rather has, as viewed three-dimensionally, a non-uniformprofile along the X-Y axis or, in addition thereto, also a non-uniformshape along the Z axis, cooling capacities of a cooling member and amold member must be controlled in order to prevent formation of cracksin the resultant cast ingot, which are caused by the solidificationinterface being depressed locally; and to prevent formation of internaldefects, such as blowhole defect and microshrinkage, which are generatedwhen the solidification interface forms a closed surface within a castingot.

[0040] When a cooling member is excessively thin, rigidity of thecooling member lowers. Thus, heat cycle imposed upon each castingprocess distorts the cooling member, resulting in deformation thereof,and producing cast ingots of undesired shape. Furthermore, thermal shockor deterioration of the material of the cooling member produces cracksin the cooling member through which a cooling water leaks, leading todisturbed operation of the apparatus. Thus, in order to continue thecasting process for a long period in a stable manner, the coolingcapacity and the rigidity of the cooling member must be enhanced.

[0041] To this end, the cooling member is thickened so as to enhance therigidity, and in addition, unevenness is provided on an outer surface ofthe cooling member and a cooling medium is supplied to the outer surfaceof the cooling member, whereby the contact area between theunevenness-imparted portion and the cooling medium (hereinafter referredto as “cooling-medium-contact-area”) is enhanced, leading to attainmentof enhanced cooling capacity. The configuration of the unevenness is notparticularly limited, and for example, a hole which does not reach theinterior surface (blind hole) or a fin-like shape may be employed.

[0042] Usually, the cooling medium is jetted radially from a sprayingmeans such as a cooling spray. Thus, even when such unevenness isuniformly provided, the cooling-medium-contact-area of the unevenportion directly above the nozzle of the cooling spray is different fromthat of other uneven portions.

[0043] The shape of the uneven portion (or dents) is determined so as tomaintain the rigidity of the cooling member and to attain the desiredcooling capacity. Preferably, a distance of at least 1 mm is left belowthe internal surface of the cooling member. If engraving is performedfarther, rigidity of portions in the vicinity of dents cannot besecured, inviting the risk of generating cracks in the cooling member.Generally speaking, the cooling capacity of deeply engraved dents ishigher than that of shallow dents due to largercooling-medium-contact-area. Therefore, deep dents may be formed in aportion where high cooling capacity is desired, and shallow dents may beformed in a portion where low cooling capacity is desired.

[0044] The pitch of the dented portion (density of the formed dents) isdetermined in accordance with the shape of the cast ingot, and the pitchis not necessarily invariable. Depending on the case, the pitch may belong or short, and some portion may have no dents. On the other hand,when dents are formed at a certain unvaried pitch (uniform density ofdents), cooling capacity can be controlled through regulating thediameter and/or depth of the dents. Thus, for example, portions forwhich high cooling capacity is desired may be provided with dents ofnarrow pitch (high density of dents), whereas other portions for whichlow cooling capacity is desired may be provided with dents of wide pitch(low density of dents).

[0045] In particular, when holes are provided as the dents, the diameterof the holes is preferably 3 mm or more for the following reasons. Whencooling water in the form of spray or shower is jetted toward the holeseach having a diameter of less than 3 mm, cooling water entered theholes is vaporized under heat, and the steam prevents jetted coolingwater from entering the holes, lowering the cooling effect as comparedto the case in which no hole is provided. The maximum diameter isdetermined in accordance with the size of the cast ingot and the coolingcapacity profile to be attained. However, holes of any size may beformed so long as the rigidity of the cooling member is secured.Generally, large holes, realizing a large cooling-medium-contact-area,provide higher cooling capacity as compared with small holes. Thus,large holes may be provided at a site where high cooling capacity isdesired, and small holes may be provided at a site where low coolingcapacity is desired.

[0046] When the angle of the hole axis (“α”; hereinafter referred to as“inclination angle”) coincides with the collision angle (β) at which thecooling water jetted in the form of spray or shower hits the coolingmember, the maximum cooling capacity is attained. In other words, whenhigh cooling capacity is desired, the following relation is preferablysatisfied: α=β±10°. When α and β do not satisfy this relation, thecooling capacity may decrease.

[0047]FIG. 2 is a cross-sectional view showing an exemplary apparatus ofthe present invention and depicting a cooling capacity control mechanismof mode “d.” Elements identical to those shown in FIG. 1 are denoted bythe same reference numerals.

[0048] In this embodiment, molten metal is teemed through a singlemolten metal inlet 4 disposed at an approximately central portion, tothereby produce a cast ingot having an almost uniform thickness.

[0049] In this embodiment, a plurality of blind holes 9 which serve asthe uneven portion are formed at almost the same intervals in an outersurface of a cooling member 1 having an almost uniform thickness, and aspray nozzle 8 for jetting a cooling medium is disposed beneath theapproximately central portion of the cooling member 1.

[0050] As described above, holes 9 disposed directly above the spraynozzle 8, which are disposed at an approximately central position, havea larger cooling-medium-contact-area than holes 9 in peripheralportions. Thus, holes 9 disposed directly above the spray nozzle 8provide higher cooling capacity. Therefore, in the cooling member 1,cooling capacity is high in the central portion and low in theperipheral portion.

[0051] In this connection, as shown in FIG. 3 for example, when holes 9are formed in such a manner that the inclination angle a of each of theholes is identical with its corresponding collision angle β of thecooling medium, the maximum cooling capacity can be obtained.

[0052] The aforementioned controlling methods can be performedindependently one from another, and they may be appropriately combinedin accordance with needs. For example, the aforementioned modes “a” and“d” are combined, to thereby use a cooling member in which the thicknessvaries from portion to portion, and an outer surface thereof ispartially provided with unevenness by means of holes, fins, etc.

[0053]FIG. 4 shows an embodiment in which molten metal is teemed througha molten metal inlet 4 disposed at an approximately central position andthe cast ingot has a thick wall in the central to right portion (asviewed in the drawing) and a thin wall in the left portion (in thedrawing).

[0054] The cooling member 1 of the present embodiment is designed suchthat the central to right portions, which correspond to the thickerportion of the cast ingot in which the solidification rate of moltenmetal 6 is slow, are formed to have a thin wall so as to lessen the heatcapacity, and the thus-formed thin wall is provided with unevennessthrough formation of a plurality of holes 9 so as to increase the areathat can contact a cooling medium jetted from a cooling spray 8 disposedbelow an approximately central portion of the cooling member 1, tothereby enhance the cooling capacity of the central portion and theright portion. In particular, the holes 9 are formed in such a mannerthat the inclination angles of the holes 9 coincide with correspondingcollision angles of the cooling medium. In addition, the left portion ofthe cooling member 1, which corresponds to the thinner portion of thecast ingot in which molten metal solidifies faster, is thickened, and nohole 9 is formed in the left portion, to thereby lower the coolingcapacity of the left portion.

[0055] e. Mode in Which a Cooling Medium Jetted in the Form of Spray orShower from a Plurality of Nozzles Hits an Outer Surface of a CoolingMember (Claim 8);

[0056]FIG. 5(c) shows an exemplary apparatus according to mode “e” inwhich molten metal is teemed through two molten metal inlets 4 providedon the right side and the left side, to thereby produce a connecting rodmember having a more complicated three-dimensional shape as shown inFIGS. 5(a) and 5(b).

[0057] In casting of such a product, a significant amount of moltenmetal 6 is accumulated in hemispheres directly below the two moltenmetal inlets 4, and the molten metal in the hemispheres has high heatcapacity. Thus, the portion of the cast ingot directly below the twomolten metal inlets 4 tends to generate cracks because local depressionscorresponding to the two molten metal inlets 4 are produced in thesolidification interface directly below the inlets 4. On the other hand,the space within the arm portion connecting the hemispheres is narrowand can contain less molten metal.

[0058] In order to cope with this problem, the cooling member 1 of thepresent embodiment has been designed such that specific portions of thecast ingot directly below the two hemispheres, in which the molten metal6 solidifies slower, is thinned, and the thinned portion is providedwith unevenness through formation of a plurality of holes 9, towardwhich a cooling medium is jetted from two spray nozzles 8, 8 disposed atlocations corresponding to the locations of the hemispheres, to therebyenhance the cooling capacity of the portions directly below the twohemispheres. Moreover, the portion of the cooling member directly belowthe arm portion of the cast ingot, in which the molten metal 6solidifies faster, is thickened, and the thickened portion is providedwith no unevenness; i.e., no holes 9, to thereby lower the coolingcapacity of the portion directly below the arm portion. Notably, theconnecting rod member produced by use of the present apparatus isdrilled at points corresponding to the locations of the molten metalinlets 4 on the right side and on the left side as shown in FIG. 5(a).

[0059] The present embodiment has been described as an embodiment ofmode “e.” However, the present embodiment is also an embodimentaccording to the aforementioned mode “a” since the thickness of thecooling member 1 is locally varied, and is also an embodiment accordingto the aforementioned mode “d” since an unevenness (holes 9) isprovided. The same applies, throughout the following embodiments, andeven when any of the aforementioned modes is used in combination, noparticular mention may be given.

[0060] FIGS. 6(a) and 7(a) are views showing other exemplary apparatusesfor casting connecting rod members having a shape identical to thatshown in FIG. 5. In both embodiments, molten metal is teemed through onemolten metal inlet 4.

[0061] In the apparatus shown in FIG. 6(a), molten metal is teemedthrough one molten metal inlet 4 disposed at an approximately centralposition; and a cooling member 1 is formed in such a manner that theportion directly below the arm portion, in which solidification of themolten metal 6 delays, is thinned, and that the thinned portion isprovided with unevenness through formation of a plurality of holes 9,toward which a cooling medium is jetted from a single spray nozzle 8disposed at an approximately central position, to thereby enhance thecooling capacity of the portion directly below the arm portion.Moreover, the portions of the cooling member 1 directly below the rightand left hemispheres are thickened outwardly; and the thickened portionis provided with no unevenness; i.e., no holes 9, to thereby lower thecooling capacity of the portions directly below the hemispheres. In thisconnection, the connecting rod member cast by use of the presentapparatus is drilled at an approximately central portion correspondingto the location of the molten metal inlet 4 as shown in FIG. 6(b).

[0062] In the apparatus shown in FIG. 7(a), molten metal is teemedthrough one molten metal inlet 4 disposed on the left side; and acooling member 1 is formed in such a manner that the portion directlybelow the left hemisphere, in which solidification of molten metal 6delays, is thinned, and that the thinned portion is provided with aplurality of holes 9 serving as the uneven portion, and a cooling mediumis jetted from a single spray nozzle 8 disposed on the left side, tothereby enhance the cooling capacity of the portion directly below theleft hemisphere. Moreover, the portion directly below the central armportion and the right hemisphere is thickened outwardly; and thethickened portion is provided with no uneven portions; i.e., no holes 9,to thereby lower the cooling capacity of the portion directly below thecentral arm portion and the right-side hemisphere. The portion directlybelow the arm portion, through which molten metal is introduced into theright-side hemisphere, is particularly thickened. In this connection,the connecting rod member cast by use of the present apparatus isdrilled at a single point on the left side corresponding to the locationof the molten metal inlet 4 as shown in FIG. 7(b).

[0063] As described above, when the number and the location of moltenmetal inlet(s) are varied for cast ingots of the same shape, the coolingcapacity control mechanism is modified accordingly, and cooling capacitycan be appropriately controlled and adjusted. Thus, the critical pointis to carry out solidification so that the solidification interfaceadvances to reach an inner end of the mold, to thereby produce a castingot having no cut surface or riser portion.

[0064] f. Mode in Which Unevenness is Provided Through Formation ofBlind Holes in Such a Manner that Inclination Angles Differ fromCorresponding Collision Angles of a Cooling Medium Jetted in the Form ofSpray or Shower and Supplied to the Outer Surface of the Cooling Member(Claim 10);

[0065] Holes are formed in a portion of an outer surface of a coolingmember in such a manner that inclination angles of the holes differ fromcorresponding collision angles of a cooling medium in the form of sprayor shower so as to prevent direct entering of the cooling medium intothe holes. In this manner, the cooling capacity of the aforementionedportion is lowered, and well-balanced cooling capacity can be attainedthroughout the cooling member, contributing to formation of asolidification interface of desired shape.

[0066] The relationship between inclination angle α of the hole andcollision angle β of the cooling medium is preferably α>β±≅10°.

[0067] When the cooling medium does not enter the holes, the holes arecooled mainly through air-cooling, resulting in lower cooling capacityas compared with the case in which no holes are formed.

[0068] For example, in the aforementioned embodiment shown in FIG. 2,holes 9 in both the central portion and the peripheral portion of thecooling member 1 are vertically formed and have almost the same depth.However, the cooling medium can enter deeply in holes 9 in the centralportion because the inclination angle a virtually coincides with thecollision angle β of the cooling medium, leading to largecooling-medium-contact-area, which enhances the cooling capacity of thecentral portion, whereas the cooling medium is prevented frompenetrating deeply in holes 9 in the peripheral portion because theinclination angle α significantly differs from the collision angle β ofthe cooling medium, resulting in lowered cooling capacity at theperipheral portion.

[0069] g. Mode in Which a Portion of an Outer Surface of a CoolingMember is Provided with Means for Preventing the Cooling Member fromContacting a Cooling Medium (Claims 11 and 12);

[0070] As described above, forced cooling of a cooling member isperformed through a method in which a cooling medium is supplied to anouter surface of the cooling member. In combination with this method, aportion of the outer surface of the cooling member is provided with astep, or a restriction plate for restricting the spray direction of thecooling medium is installed, to thereby prevent the cooling medium fromcontacting a portion of the cooling member. Thus, since the coolingcapacity resulting from the heat of vaporization of the cooling mediumdecreases (masking effect), well-balanced cooling capacity can beattained throughout the cooling member, contributing to formation of asolidification interface of desired shape.

[0071]FIGS. 8 and 9 are cross-sectional views showing exemplaryapparatuses of the present invention and depicting the cooling capacitycontrol mechanisms of modes “f” and “g.” Elements identical to thoseshown in FIG. 1 are denoted by the same reference numerals.

[0072] Although the cast ingots schematically shown in FIGS. 8 and 9 maylook similar to the cast ingot shown in FIG. 1, in the presentembodiments, molten metal is teemed through a molten metal inlet 4disposed at an approximately central position, and the cast ingots inthe present embodiments are of a disk shape and have an almost uniformthickness which is extremely smaller than the outer diameter.

[0073] In such a casting process, in which the thickness of the castingot is extremely smaller than the outer diameter, an idealunidirectional solidification state cannot be maintained because thetime requires for solidification of the center portion is different fromthat required for solidification of the peripheral portion; i.e., theremotest portion from the molten metal inlet 4. Thus, the center portionof the cast ingot easily generates cracks.

[0074] In order to cope with this problem, in the present embodiment,blind holes 9 serving as unevenness are formed in a central outersurface of a cooling member 1 in such a manner that the inclinationangles coincide with corresponding collision angles of a cooling medium,to thereby considerably enhance the cooling capacity. On the other hand,interior spaces 13 (in FIG. 9, material sections 14 having a differentthermal conductivity) are provided in a peripheral portion in such amanner that the interior space 13 expands toward the periphery.Moreover, a spray nozzle 8 is provided with a restriction plate 15 forrestricting the spray direction of a cooling medium so as to prevent thecooling medium from contacting the outer surface of the interior spaces13 (the material sections 14). Moreover, a step 16 is provided in aintermediate portion of the slope surrounding the central portion so asto prevent the cooling medium from running down along the slope, tothereby considerably lower the cooling capacity.

[0075] h. Mode in Which a Portion of an Outer Surface of a CoolingMember is Covered with a Heat-Insulating Material (Claims 11, 13, and14);

[0076] As described above, forced cooling of a cooling member isperformed through a method in which a cooling medium is supplied to anouter surface of the cooling member. In combination with this method, aportion of the outer surface of the cooling member is covered with aheat-insulating material so as to prevent the portion from contactingthe cooling medium, to thereby lower the cooling capacity attainedthrough evaporation heat of the cooling medium (masking effect); and toprevent heat from radiating from the outer surface of the cooling member(insulation effect). Thus, well-balanced cooling can be attainedthroughout the cooling member, contributing to formation of asolidification interface of desired shape.

[0077] Examples of the heat-insulating material include heat-insulatingrubber, ceramic material, heat-insulating material made of fireretardant fibers or non-combustible fibers.

[0078]FIG. 10 is a cross-sectional view showing an exemplary apparatusof the present invention and depicting a cooling capacity controlmechanism of mode “h.” Elements identical to those shown in FIG. 1 aredenoted by the same reference numerals.

[0079] In the present embodiment, molten metal is teemed through amolten metal inlet 4 disposed on the left side, to thereby produce acast ingot in which the left and center portions (as viewed in thedrawing) are thicker and the right portion (as viewed in the drawing) isthinner.

[0080] In such a casting process, the left portion and the centerportion of the cast ingot tend to generate cracks for the followingreasons: the left portion and the center portion of the cast ingot,which are thick, have large heat capacity; and solidification of moltenmetal 6 in the left portion and the center portion delays because themolten metal inlet 4 is provided on the left side.

[0081] In order to cope with this problem, a cooling member 1 of thepresent embodiment is designed in the following manner. A plurality ofholes 9, which serve as unevenness, are formed in the left portion andthe center portion, toward which a cooling medium is jetted from acooling spray 8 disposed below the holes 9, to thereby enhance thecooling capacity of the left portion and the center portion; and aheater 11 is incorporated into the right portion, and an outer surfaceof the right portion is covered with a heat-insulating material 12 so asto prevent the cooling medium from contacting the outer surface, tothereby lower the cooling capacity of the right portion.

[0082] 2. Mode in Which a Circulation Passage for a Cooling Medium isIncorporated into a Portion of a Cooling Member (Claims 15 and 16);

[0083] In mode 1 wherein an outer surface of a cooling member is cooledthrough contacting a cooling medium thereto, at least one of modes“a”-“h” must be employed in combination. In contrast, the present methodcan attain local cooling of the cooling member without employing such amode in combination. Needless to say, the aforementioned mode may beused in combination in accordance with the shape of the cast ingot.

[0084] The diameter, location, shape, and depth from the upper surfaceof a circulation passage for the cooling medium are determined inaccordance with the required cooling capacity. Flow rate and timings toinitiate or terminate cooling are determined in accordance with theshape of the cast ingot. Examples of the cooling medium include, similarto the cooling medium for supplying to an outer surface of a coolingmember as in the aforementioned mode, water, supercooled water of 0° C.or lower (e.g., supercooled water of 0° C. or lower containing 0.5% ormore sodium chloride, or supercooled water of 0° C. or lower containinga substance such as ethylene glycol), and an oil.

[0085]FIG. 11 is a cross-sectional view showing an exemplary apparatusof the present invention and depicting a cooling capacity controlmechanism of mode 2. Elements identical to those shown in FIG. 1 aredenoted by the same reference numerals.

[0086] In the present embodiment, molten metal is teemed through amolten metal inlet 4 disposed on the left side, to thereby produce acast ingot in which the right portion and the center portion (in thedrawing) is thicker, and the left portion (in the drawing) is thinner.

[0087] In such a casting process, the right portion of the cast ingot,which is thick, is high in heat capacity, whereas the left portion,which is thin, is disposed directly below the molten metal inlet 4.Thus, each portion involves a factor which can cause crack formation.

[0088] In order to cope with this problem, the cooling member 1 of thepresent embodiment is designed such that a plurality of holes 9, whichserve as unevenness, are formed in the right-side portion, toward whicha cooling medium is jetted from a single spray nozzle 8 disposed belowthe holes 9, and a circulation passage 10 through which a cooling mediumflows is incorporated into the left portion, to thereby regulate thecooling capacity of respective portions through controlling theircorresponding forced cooling mechanisms appropriately.

[0089] 3. Mode in Which a Temperature-Controlled Cooling Medium isBrought into Contact with a Cooling Member (Claim 17);

[0090] As described above, the cooling medium is selected from water,supercooled water of 0° C. or lower, a volatile liquid, and an oil, eachof which can be used singly or in combination. Needless to say, thecooling capacity of water at room temperature is different fromsupercooled water of 0° C. or lower. In other words, the coolingcapacity can be controlled through controlling the temperature of acooling medium.

[0091] An exemplary method for attaining this purpose will be describedwith reference to the embodiment shown in FIG. 5, wherein the coolingmedium jetted through the spray nozzles 8 on the right side and thatjetted through the spray nozzles 8 on the left side are controlled tohave different temperatures from each other. In this case, for example,room-temperature water is jetted from the right side, and supercooledwater of 0° C. or lower is jetted from the left side, to thereby controlthe cooling capacity of the cooling member 1 such that the coolingcapacity of the portion directly below the left hemisphere is higherthan that of the right portion. In this manner, balancing in coolingcapacity can be more precisely controlled between the left portion andthe right portion.

[0092] 4. Mode in Which Contact History of a Cooling Medium with aCooling Member is Controlled (Claim 18);

[0093] Needless to say, cooling capacity differs between the two cases;continuous contact between the cooling medium and the cooling member andintermittent contact therebetween. By the term “intermittent contact” ismeant that contacting state and non-contacting state occur alternately,and thus, cooling capacity can also be controlled through controllingthe ratio of contact time to non-contact time. In other word, coolingcapacity can be regulated by modifying the contact history between acooling medium and a cooling member.

[0094] For example, in the aforementioned embodiments shown in FIGS. 8and 9, restriction plate 15, which regulates the spray direction, ismade movable and a control mechanism (not shown) for controlling themotion of the restriction plate 15 is connected thereto. In this manner,cooling capacity can be enhanced as compared with the case in which thecooling medium does not at all contact the outer surface of the interiorspace 13 (material section 14). As a result, balance of coolingcapacities between the center portion and the peripheral portion of thecooling member 1 is controlled more precisely.

[0095] 5. Mode in Which a Heater is Incorporated into a Portion of aCooling Member (Claims 19 and 21);

[0096] Forced cooling of a cooling member is effected through a methodin which either or both of the aforementioned modes 1 and 2 areimplemented, and is controlled through implementing either or both ofthe aforementioned modes 3 and 4 in accordance with needs. Incombination with the forced cooling, a heater for lowering coolingcapacity is buried in a portion of a cooling member, to thereby blockheat flow from molten metal to the outer surface of the cooling member.As a result, well-balanced cooling can be attained throughout thecooling member, contributing to formation of a solidification interfaceof desired shape.

[0097] The heater may be a resistance heater, superheated steam, orhigh-temperature gas.

[0098] As describe above with reference to, for example, FIG. 10, theleft portion and the center portion of the molten metal 6 solidifiesslowly, since in these portions the cast ingot is thick and the moltenmetal inlet 4 is disposed, and therefore, an attempt is made to enhancethe cooling capacity of these portions. In contrast, the molten metal 6in the right portion solidifies faster because the right portion of thecast ingot is thinner and is remote from the molten metal inlet 4. Inorder to attain a well-balanced cooling, the heater 11 is incorporatedinto the right portion, and the outer surface of the right portion iscovered with the heat-insulating material 12 so as to prevent thecooling medium from contacting the outer surface of the right portion,to thereby lower the cooling capacity of the right portion.

[0099] 6. Mode in Which a Heater is Incorporated into a Portion of aMold Member (Claims 20 and 21);

[0100] Forced cooling of a cooling member is effected through a methodin which either or both of the aforementioned modes 1 and 2 isimplemented, and the forced cooling is controlled through implementingeither or both of the aforementioned modes 3 and 4 in accordance withneeds. In combination with the forced cooling, a heater for lowering thecooling capacity is buried in a portion of a mold member, to therebyblock heat flow from molten metal to the mold member. As a result,well-balanced cooling capacity can be attained throughout the coolingmember, contributing to formation of a solidification interface ofdesired shape.

[0101] The aforementioned mode 5 is effective when a portion of castingot that lowers cooling capacity is relatively thin. When such aportion is relatively thick, solidification performance is affected bynot only the cooling member but also the mold member, and therefore, aheater is incorporated into the mold member. The location of theincorporated heater is either or both of a side section and an uppersection of the mold member. The mold may be divided into a side memberand an upper member.

[0102] The heater may be a resistance heater, superheated steam, or ahigh-temperature gas.

[0103]FIG. 12(b) is a cross-sectional view showing an exemplaryapparatus of the present invention and depicting a cooling capacitycontrol mechanism of mode 6. Elements identical to those shown in FIG. 1are denoted by the same reference numerals.

[0104] The shape of the cast ingot in this embodiment is such that thickportions A and B are formed on the right side and left side (as viewedin the drawing), respectively, with a thin portion being interposedtherebetween, and molten metal is teemed through a molten metal inlet 4disposed at an upper end of left-hand space B providing a thicker ingotportion.

[0105] In such casting, molten metal filled in the smaller space A,which is remote from the molten metal inlet 4, solidifies faster thanmolten metal filled in the space B. While waiting for the completion ofsolidification of molten metal in space B, the mold material thatdefines space A is deprived of heat through the solidified cast ingot inspace A, and therefore, the temperature of the side wall and upper wallof the mold member constituting space A becomes lower than the moltenmetal temperature. Since the molten metal in direct contact with themold begins to solidify from the wall surfaces of the mold, the finalsolidification portion ris generated within the cast ingot in space A asshown in FIG. 12(a), leading to a defective cast ingot including ablowhole or microshrinkage in the portion corresponding to the finalsolidification portion.

[0106] In order to cope with this problem, as shown in FIG. 12(b), aheater 11 is buried in the mold material at the location directly abovethe space A so as to add heat commensurate with the amount of heatremoved through the cast ingot, to thereby heat the mold to atemperature higher than the molten metal temperature. As a result,solidification of the molten metal proceeds without producing a closedsolidification interface within the space A, and solidification iscompleted with the solidification interface coinciding with the interiorupper surface of the mold. Thus, a wholly non-defective cast ingot canbe obtained.

[0107] The heating conditions are preferably monitored throughtemperature measurement by means of a thermocouple buried in arepresentative position of the mold, to thereby maintain thesolidification interface in a predetermined shape. The heater ispreferably connected to a power source and a control box in order tocontrol the heater automatically.

[0108] Unlike the case of application of heat by a heater, cooling doesnot provide any negative energy. However, in either of theaforementioned modes (1-b and 1-c) in which a space or a materialsection of different thermal conductivity is provided within the coolingmember and the aforementioned mode (1-f) in which the inclination angleof holes formed in an outer surface of a cooling member is controlled inaccordance with the collision angle of a cooling medium, similar to thecase in which a heater is provided (modes 5 and 6), prevention of heatfrom flowing from the molten metal to the outer surface of the coolingmember can be realized.

[0109]7. Mode in Which a Plurality of Heating Sections and CoolingSections are Provided Within a Cooling Member, and the Functions of theRespective Sections are Controlled (Claim 22);

[0110] When a mechanism which can be arbitrarily used for heating andcooling in accordance with needs is installed within a cooling member inadvance, the temperature of an arbitrary portion of the cooling membercan be arbitrarily controlled. Preferably, the heating section issimilar to the aforementioned heater which performs heating in anarbitrary manner. The cooling section is a section or a chamber to whichthe aforementioned cooling medium is to be supplied, and preferablyperforms cooling in an arbitrary manner. These sections controltemperatures (cooling capacity) of respective portions of the coolingmember in accordance with the shape of the cast ingot and the number andthe location of the molten metal inlet.

[0111]FIG. 13 is a cross-sectional view showing an exemplary apparatusof the present invention and depicting a cooling capacity controlmechanism of mode 7. Elements identical to those shown in FIG. 1 aredenoted by the same reference numerals.

[0112] In the present embodiment, molten metal is teemed through amolten metal inlet 4 disposed at an approximately central position, tothereby produce a disk-shaped cast ingot having a shape similar to thoseshown in FIGS. 8 and 9; i.e., a cast ingot having a virtually uniformthickness wherein the thickness is extremely smaller than the outerdiameter.

[0113] In such casting, as described above, the thickness of the castingot extremely smaller than the outer diameter causes solidificationtime difference between the center portion and the peripheral portion;i.e., the remotest portion from the molten metal inlet 4, of the disk.Thus, the center portion of the cast ingot easily produces cracksbecause an ideal unidirectionally solidification state cannot bemaintained.

[0114] In order to cope with this problem, cooling sections (chambers)19, which are provided independently from one another and each beingconnected to a cooling control unit 20, are disposed in an upper innerportion of a cooling member 1 of the present embodiment; and heatingsections (chambers) 21, which are provided independently from oneanother and each being connected to a heating control unit 22, aredisposed in a lower inner portion of the cooling member 1. The coolingcontrol unit 20 can supply a cooling medium to an arbitrary coolingsection 19, and the heating control unit 22 can make an arbitraryheating section 21 generate heat.

[0115] In this case, the cooling control unit 20 supplies the coolingmedium to the cooling sections 19 that cool a center portion below themolten metal inlet 4, and supplies no cooling medium to the othercooling sections 19; and the heating control unit 22 make only theheating sections 21 that heat a peripheral portion of the disk generateheat.

[0116] In this manner, the cooling member 1 of the present embodimentshown in FIG. 13 can be appropriately applied to a cast ingot of anyshape as long as the lower surface of the cast ingot is flat.

[0117] In the present invention, through use of a cooling capacitycontrol mechanism that locally enhances or lowers cooling capacity of acooling member or controls local heat removal through intentionalheating in accordance with the shape of the cast ingot and the locationand the number of the molten metal inlet—specifically, through theaforementioned method 1 (“a”-“h”) and 2 to 6, or appropriate combinationthereof—control and regulation of solidification of a cast ingot isattained without producing a closed loop of solidification interfacewithin the mold. The cast ingot obtained in the aforementioned mannerdoes not include any riser portion or cut surface. Preferably, uppercorners of the cast ingot has a radius of curvature of 1 mm or less.

[0118] Therefore, the cast ingot obtained through the aforementionedmethod and apparatus is a non-defective product having no cracks,blowhole defects, or internal defects, and can, of course, directlyserve as a product (casting), or can be used as a material for plasticworking for use in various processing such as forging.

[0119] Furthermore, according to the present invention, a mechanism maybe provided for opening at least a portion (a portion or the entirety)of a cooling member in the course of solidification of molten metalwithin a mold; and a mechanism for supplying a cooling medium directlyto an exposed outer surface of a cast ingot (claim 23).

[0120] The cast mechanism in the vicinity of a cooling member is finerbecause molten metal solidifies faster. As the solidification interfaceproceeds remote from the cooling member, the solidification ratedecreases. In other words, when a cooling member is used for cooling,the thicker the cast ingot, the larger the solidification ratedifference between at a lower section and at an upper section of a castingot, resulting in wide cast mechanism difference, which leads todifference in terms of cast quality or forging property. Furthermore,the upper section of the cast ingot is apt to generate internalmicroshrinkage and forging cracks.

[0121] The cooling capacity attained through indirect cooling by use ofa cooling member is inferior to that of direct cooling in which acooling medium is directly applied to the lower surface of a cast ingot.However, without using a cooling member, the aforementioned localcontrol of heat removal from a mold member containing a cooling membercannot be performed. Thus, it is preferable to combine indirect coolingby use of a cooling member and direct cooling in order to enhance thecooling capacity.

[0122] At the beginning of casting, a cooling member, which serves as aportion of a mold, receives molten metal. For example, in the course ofsolidification, all or a portion of the cooling member contacting thelower surface of a cast ingot is opened, to thereby apply a coolingmedium, which has been cooled the outer surface of the cooling member,directly to the lower surface of the cast ingot by means of coolingspray. As a result, the amount of heat removed from the cast ingotsignificantly increases, and the cooling rate and the solidificationrate increase. In this manner, a cast ingot having small metallographicdifference between an upper portion and a lower portion can be obtained.Alternatively, the cooling member may be lowered, after which arotatable apparatus comprising a spray device and a pan for collectingthe cooling medium may be used. In this case, the cast ingot is held soas not to fall, in a manner appropriate for ingot and the mold in termsof shape.

[0123] The present method is particularly effective when the ingot to becast is thick, and enables casting of any species of alloy withoutinvolving difficulties associated with a conventional casting of analloy.

[0124]FIG. 14 is a cross-sectional view showing an exemplary apparatusof the present invention in which a cooling member 1 is composed of aplurality of members 1 a and 1 b. The member 1 b is connected to adriving means 18 via a piston rod 17 so that the member 1 b can slidablymove while contacting the lower surface of the member 1 a.

[0125] The casting operation performed by use of the present apparatusis as follows.

[0126] During teeming of molten metal 6, the member 1 b is placed at aposition (1) in order to close a hole in the member 1 a. Subsequently,the molten metal 6 in a mold 2 is solidified from the upper surface ofthe cooling member 1 by means of a cooling spray (spray nozzle 8) andthe cooling member 1.

[0127] When the solidification interface 6 b in the mold 2 has reachedthe position denoted by @, the driving means 18 is started to operate inorder to slide the member 1 b to the position (2) to thereby expose thelower surface of the cast ingot, to which a cooling medium is directlysprayed.

[0128] After completion of solidification, the cooling member 1 islowered, and the cast ingot is removed.

[0129] As described above, the cooling member may comprise a pluralityof members.

[0130] Each member constituting the cooling member is made of any of theaforementioned materials, and the member may be made up of homogeneousor heterogeneous material(s).

[0131] Preferably, respective members are processed to have optimalshapes from the viewpoints of rigidity and cooling capacity. A hole orholes may be formed in each member, or no hole may be formed, and thethickness may be controlled in an appropriate manner.

[0132] The driving means may be any apparatus such as an air cylinder, ahydraulic cylinder, or an electric cylinder. Although the driving meansshown in FIG. 14 moves up and down along with the cooling member, themechanism of the driving means is not limited thereto.

[0133] A series of operations of casting-related apparatus may beperformed through a timer control in accordance with a predeterminedtime table, or alternatively, a measuring means such as a thermocouplemay be inserted into a cooling member and/or a side and/or upper wall(s)of the mold so as to measure and monitor the temperature of respectiveportions, and the operation of each apparatus is started when thetemperature has reached a predetermined point.

[0134] In particular, when a movable portion (member 1 b in theillustrated embodiment) is opened excessively early, unsolidified moltenmetal flows out into a cooling case including a cooling spray, whereaswhen the movable portion is opened excessively early, microshrinkage isproduced within the mold and the crystal grains become coarse.

[0135] When the movable portion (the member 1 b in the illustratedembodiment) is opened, the cast ingot which is being solidified shouldnot fall from the mold, and therefore, the cast ingot is designed tohave a shape for allowing the ingot of as-cast shape to be retained bythe mold, as shown in FIG. 14. Alternatively, it is also effective toprovide, to a fixed portion (member la in the illustrated embodiment), aprojection which does not impede the removal operation for the castingot. The projection, which forms a depression in a product, shouldhave a shape which does not cause any problem during use of the castingot.

[0136] This method can be used in combination with the aforementionedvarious cooling control methods. Needless to say, the methods arepreferably combined in accordance with the species of the alloy and theshape of the cast ingot, to thereby provide optimal operationalconditions.

[0137] [Embodiments]

[0138] [Embodiment 1]

[0139] An aluminum alloy was melted in a separately provided meltingfurnace, and the molten metal was cast by use of the apparatus ofFIG. 1. The thus-obtained cast ingot was examined for metallographicmicrostructure. The cooling member is made of copper, and the mold, themolten metal reservoir, and the open/close plug were made of acommercially available refractory heat-insulating material (Lumiboard;product of Isoraito Kogyo Kabushiki Kaisha). A liner was insertedbetween the side mold 2 b and the upper mold 2 a, to thereby secure agas ventilation of the mold. The upper surface of the cooling member hasa step-down center, and the slope angle of the step-down portion is 45°.The cast ingot to be produced has a disk shape having a convex portionin its lower surface, an outer diameter of 62.5φ, an outer thickness atthe periphery of 7 mm, a diameter of the central thick portion of 30φ,and a thickness of the central thick portion of 12 mm. The coolingmember has an outer shape depressed to form a hollow cone toward thecenter. The central portion of the cooling member has an inner diameterof 30φ and a thickness of 5 mm. The thickness of the cooling memberincreases at 45° from the edge of the central portion toward theperiphery. The casting conditions and the procedure are as follows.

[0140] 1) Alloy species: JIS 2218 alloy

[0141] 2) Temperature of molten metal contained in the molten metalreservoir: 720° C.

[0142] 3) Cooling member temperature before teeming: 150° C.

[0143] 4) Flow rate of cooling water: 5 liters/minute

[0144] 5) Diameter of molten metal inlet: 12φ

[0145] 6) Casting procedure:

[0146] Close the molten metal inlet with the open/close plug two secondsafter initiation of teeming.

[0147] Start water cooling when the cooling member temperature hasreached 500° C.

[0148] Stop water cooling when the cooling member temperature hasreached 30° C.

[0149] Start descending of the cooling member when the cooling membertemperature has reached 200° C.

[0150] 7) The cast body was allowed to fall spontaneously together withthe cooling member, and then collected.

[0151] [Embodiment 2]

[0152] The apparatus as shown in FIG. 2 was used, and cracks in thecooling member were investigated. The cooling member has a thickness of12 mm, a hole diameter of 4φ, and a hole depth of 10 mm. The holes wereprovided at nodes of 7 mm×7 mm grid. The casting conditions and theprocedure were the same as in Embodiment 1. The cast ingot to beproduced has an outer diameter of 62.5φ and a thickness of 9 mm.

[0153] [Embodiment 3]

[0154] The apparatus as shown in FIG. 11 including a passage forcirculating a cooling medium within the cooling member was used in orderto produce a cast ingot having a three-dimensionally complicated shapewith no plane of symmetry. The cast ingot to be produced has a thickness(thinner portion) of 9 mm, a thickness (thicker portion) of 15 mm, alongest edge of 50 mm, and a shortest edge of 35 mm. The castingconditions and the procedure are as follows.

[0155] 1) Alloy species: JIS 6061 alloy

[0156] 2) Temperature of molten metal contained in the molten metalreservoir: 720° C.

[0157] 3) Cooling member temperature before teeming: 100° C.

[0158] 4) Flow rate of cooling water: 8 liters/minute

[0159] 5) Diameter of molten metal inlet: 10φ

[0160] 6) Casting procedure:

[0161] Close the molten metal inlet with the open/close plug threeseconds after initiation of teeming.

[0162] Start water cooling when the cooling member temperature hasreached 500° C.

[0163] Stop water cooling when the cooling member temperature hasreached 30° C.

[0164] Start descending of the cooling member when the cooling membertemperature has reached 200° C.

[0165] 7) The cast body was allowed to fall spontaneously together withthe cooling member, and then collected.

[0166] 8) The metallographic microstructure of the cast ingot wasinvestigated.

[0167] [Embodiment 4]

[0168] The apparatus as shown in FIG. 10 in which a heater was buried ina portion of the cooling member was used in order to produce a castingot having a three-dimensionally complicated shape with no plane ofsymmetry. The cast ingot to be produced had a thickness (of the thinnerportion) of 9 mm, a thickness (of the thicker portion) of 15 mm, alongest side of 50 mm, and a shortest side of 35 mm. The castingconditions and the procedure are as follows.

[0169] 1) Alloy species: JIS AC2B alloy

[0170] 2) Temperature of molten metal contained in the molten metalreservoir: 720° C.

[0171] 3) Cooling member temperature before teeming: 150° C.

[0172] 4) Flow rate of cooling water: 8 liters/minute

[0173] 5) Diameter of molten metal inlet: 10φ

[0174] 6) Casting procedure:

[0175] Close the molten metal inlet with the open/close plug threeseconds after initiation of teeming.

[0176] Start water cooling when the cooling member temperature hasreached 500° C.

[0177] Stop water cooling when the cooling member temperature hasreached 30° C.

[0178] Start descending of the cooling member when the cooling membertemperature has reached 200° C.

[0179] 7) The cast body was allowed to fall spontaneously together withthe cooling member, and then collected.

[0180] 8) Heater capacity: 5 kW

[0181] 9) The metallographic microstructure of the cast ingot wasinvestigated.

[0182] [Embodiment 5]

[0183] A material used for forging a VTR cylinder drum was produced byuse of the apparatus of FIG. 8. The casting conditions and the procedureare as follows.

[0184] 1) Alloy species: JIS 2218 alloy

[0185] 2) Temperature of molten metal contained in the molten metalreservoir: 720° C.

[0186] 3) Cooling member temperature before teeming: 150° C.

[0187] 4) Flow rate of cooling water: 5 liters/minute

[0188] 5) Diameter of molten metal inlet: 12φ

[0189] 6) Dimensions of the cast ingot: 62.5φ (outer diameter)×7 mm(thickness)

[0190] 7) Casting procedure:

[0191] Close the molten metal inlet with the open/close plug 1.5 secondsafter initiation of the teeming.

[0192] Start water cooling when the cooling member temperature hasreached 500° C.

[0193] Stop water cooling when the cooling member temperature hasreached 30° C.

[0194] Start descending of the cooling member when the cooling membertemperature has reached 200° C.

[0195] 8) The cast body was allowed to fall spontaneously together withthe cooling member, and then collected.

[0196] 9) Height of the step provided on the outer surface of thecooling member: 5 mm

[0197] 10) Slope angle of the outer surface of the cooling member: 45°

[0198] 11) Thickness between the inner surface of space 13 and the topsurface or the lower surface of the cooling member: 4 mm

[0199] 12) Difference between the spray collision angle β and the holeinclination angle: within 10°

[0200] 13) The incidence of cracks of the cast ingot was investigated.

COMPARATIVE EXAMPLE 1

[0201] Casting was performed by use of the apparatus of FIG. 15 and acooling member having a flat outer surface, a thickness of 10 mm, adiameter of the central depressed portion of 30 mm, and a depth of thecentral depressed portion of 5 mm. The casting conditions and theprocedure were the same as in Embodiment 1.

[0202] The results of comparison of the thus-obtained cast ingot withthe cast ingot obtained from Embodiment 1 are as follows.

[0203] Embodiment 1: No defect was observed directly below the moltenmetal inlet.

[0204] Comparative Example 1: A defect was observed directly below themolten metal inlet.

COMPARATIVE EXAMPLE 2

[0205] Casting was performed by use of the apparatus of FIG. 15 and acooling member having a thickness of 5 mm. The casting conditions andthe procedure were the same as in Embodiment 2.

[0206] The results of comparison of the thus-obtained cast ingot withthe cast ingot obtained from Embodiment 2 are as follows.

[0207] Embodiment 2: No crack was observed in the cooling member.

[0208] Comparative Example 2: Cracks were observed in the centralportion of the cooling member.

COMPARATIVE EXAMPLE 3

[0209] Casting was performed by use of the apparatus of FIG. 15including a cooling member having no mechanism for enhancing coolingcapacity. The casting conditions and the procedure were the same as inEmbodiment 3.

[0210] The results of comparison of the thus-obtained cast ingot withthe cast ingot obtained from Embodiment 3 are as follows.

[0211] Embodiment 3: No defect was observed in the portion of the castingot directly below the molten metal inlet.

[0212] Comparative Example 3: Defects were observed in the portion ofthe cast ingot directly below the molten metal inlet.

COMPARATIVE EXAMPLE 4

[0213] Casting was performed by use of the apparatus of FIG. 15including a cooling member having no mechanism for enhancing coolingcapacity. The casting conditions and the procedure were the same as inEmbodiment 3.

[0214] The results of comparison of the thus-obtained cast ingot withthe cast ingot obtained from Embodiment 3 are as follows.

[0215] Embodiment 4: No defect was observed in the portion of the castingot directly below the molten metal inlet.

[0216] Comparative Example 4: Defects were observed in the portion ofthe cast ingot directly below the molten metal inlet.

COMPARATIVE EXAMPLE 5

[0217] Casting was performed by use of the apparatus of FIG. 15including a cooling member having a thickness of 5 mm. The castingconditions and the procedure were the same as in Embodiment 5.

[0218] The results of comparison of the thus-obtained cast ingot withthe cast ingot obtained from Embodiment 5 are as follows.

[0219] Embodiment 5: No crack was observed in the cast ingot.

[0220] Comparative Example 5: Cracks were observed in a center portionof the cast ingot.

[0221] [Effects of the Invention]

[0222] As described above, the metal casting method and the apparatus ofthe present invention enables a cast ingot to solidify without forming aclosed loop of solidification interface within a mold by means of acooling capacity control mechanism which is adapted to locally enhanceor lower the cooling capacity of a cooling member, or to control localheat removal through intentional heating in accordance with the shape ofthe cast ingot and the location and the number of the molten metalinlet. Thus, there can be produced non-defective cast ingots having nocrack or blowhole therein can be obtained.

[0223] In other words, the metal casting method and the apparatus of thepresent invention controls the number and the location of the moltenmetal inlet in accordance with the shape of the cast ingot to beproduced, to thereby produce healthy cast ingots of desired shape havingno internal defects, such as cracks, blowholes, and microshrincage, canbe obtained.

[0224] The cast ingots obtained through the aforementioned method andapparatus do not include any riser portion or cut surface, and can, ofcourse, be directly used for casting of products (castings), or can beused for casting of a material for plastic working which is used invarious processing such as forging.

BRIEF DESCRIPTION OF THE DRAWINGS

[0225] [FIG. 1] A schematic cross-sectional view showing an exemplarymetal casting apparatus of the present invention.

[0226] [FIG. 2] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0227] [FIG. 3] A cross-sectional view showing holes which are adaptedto maximize the cooling capacity.

[0228] [FIG. 4] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0229] [FIG. 5] (a) A plan view of a connecting rod member, (b) a sideview thereof, and (c) a schematic cross-sectional view showing anexemplary metal casting apparatus for casting the connecting rod member.

[0230] [FIG. 6] (a) A schematic cross-sectional view showing anotherexemplary metal casting apparatus for producing a member having a shapeidentical with the connecting rod member shown in FIG. 5, and (b) a planview showing the resultant connecting rod member.

[0231] [FIG. 7] (a) A schematic cross-sectional view showing anotherexemplary metal casting apparatus for producing a member having a shapeidentical with the connecting rod member shown in FIG. 5, and (b) a planview showing the resultant connecting rod member.

[0232] [FIG. 8] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0233] [FIG. 9] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0234] [FIG. 10] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0235] [FIG. 11] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0236] [FIG. 12] (a) A schematic cross-sectional view showing thesituation under which a closed loop of solidification interface isformed within the cast ingot. (b) A schematic cross-sectional viewshowing the situation under which solidification interface advances soas to reach the end portion of the mold.

[0237] [FIG. 13] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0238] [FIG. 14] A schematic cross-sectional view showing anotherexemplary metal casting apparatus of the present invention.

[0239] [FIG. 15] A schematic cross-sectional view showing a conventionalcasting apparatus making use of unidirectional solidification.

[0240] [Description of Reference Numerals]

[0241]1: cooling member

[0242]2: mold

[0243]3: molten metal reservoir

[0244]4: molten metal inlet

[0245]5: open/close plug

[0246]6: molten metal

[0247]6 a: solidified molten metal

[0248]6 b: solidification interface

[0249]6 c: unsolidified molten metal

[0250]7: molten metal in a reservoir

[0251]8: spray nozzle

[0252]9: hole

[0253]10: circulation passage

[0254]11: heater

[0255]12: heat-insulating material

[0256]13: interior space

[0257]14: portion of material having different thermal conductivity

[0258]15: restriction plate

[0259]16: step

1. A method for casting metal by charging molten metal into aclosed-space-definable mold which includes a cooling member and in whichan end surface of an open/close plug serves as a portion of an innerwall of the mold, characterized in that removal of heat from a moldmember comprising the cooling member is locally controlled in accordancewith the shape of cast ingot and the location and number of the moltenmetal inlet(s), to thereby solidify the molten metal in such a mannerthat the solidification interface advances to arrive at an end of aninner surface of the mold.
 2. The metal casting method as described inclaim 1, wherein an outer surface of at least one portion of the coolingmember is opened during the course of solidification of the molten metalin the mold, whereby cooling an outer surface of the exposed cast ingotdirectly with a cooling medium.
 3. A metal casting apparatus for castingmetal by charging molten metal into a closed-space-definable mold whichincludes a cooling member and in which an end surface of an open/closeplug serves as a portion of an inner wall of the mold, characterized bycomprising a cooling capacity control mechanism which imparts, to themold member comprising the cooling member, a heat removal profileappropriate for the shape of the cast ingot to be produced and for thenumber and position of the molten metal inlet(s).
 4. The metal castingapparatus as described in claim 3, wherein the cooling member is cooledby bringing an outer surface of the cooling member into contact with thecooling medium.
 5. The metal casting apparatus as described in claim 3or 4, wherein the cooling member has a thickness which is partiallydifferent from the thickness of the remaining portion.
 6. The metalcasting apparatus as described in any one of claims 3 to 5, wherein aspace is provided within a portion of the cooling member.
 7. The metalcasting apparatus as described in any one of claims 3 to 6, wherein thecooling member is made of a composite material of different thermalconductivites.
 8. The metal casting apparatus as described in any one ofclaims 3 to 7, further comprising at least one nozzle for jetting thecooling medium toward an outer surface of the cooling member and causingthe cooling medium in the form of spray or shower to hit the outersurface of the cooling member.
 9. The metal casting apparatus asdescribed in any one of claims 3 to 8, wherein an outer surface of thecooling member is partially provided with an unevenness so that the areathat can contact a cooling medium locally varies.
 10. The metal castingapparatus as described in claim 9, wherein the unevenness is holes whichdo not communicate with an interior surface and inclination angles ofthe holes are regulated to in accordance with collision angles of thecooling medium jetted in the form of spray or shower and supplied to theouter surface of the cooling member.
 11. The metal casting apparatus asdescribed in any one of claims 3 to 10, further comprising, on the outerface side of the cooling member, means for enabling local prevention ofthe cooling medium from contacting the cooling member.
 12. The metalcasting apparatus as described in claim 11, wherein the means forenabling prevention of the cooling medium from contacting the coolingmember is a step provided at a portion of an outer surface of thecooling member.
 13. The metal casting apparatus as described in claim11, wherein the means for enabling prevention of the cooling medium fromcontacting the cooling member is a heat-insulating material whichpartially covers an outer surface of the cooling member.
 14. The metalcasting apparatus as described in claim 13, wherein the heat-insulatingmaterial is a species or a combination of species selected from thegroup consisting of rubber, ceramic material, and fibrousheat-insulating material.
 15. The metal casting apparatus as describedin any one of claims 3 to 14, further comprising a circulation passagefor cooling medium which is provided within a portion of the coolingmember.
 16. The metal casting apparatus as described in any one ofclaims 3 to 15, wherein the cooling medium is a species or a combinationof species selected from the group consisting of water, supercooledwater of 0C or lower, a volatile liquid, or an oil.
 17. The metalcasting apparatus as described in any one of claims 3 to 16, wherein atemperature-controlled cooling medium is brought into contact with thecooling member.
 18. The metal casting apparatus as described in any oneof claims 3 to 17, wherein contact history of the cooling medium with acooling member is controlled.
 19. The metal casting apparatus asdescribed in any one of claims 3 to 18, further comprising a heaterprovided within a portion of the cooling member.
 20. The metal castingapparatus as described in any one of claims 3 to 19, further comprisinga heater provided within a portion of the mold member.
 21. The metalcasting apparatus as described in claim 19 or 20, wherein the heater isa heating device making use of ohmic-resistance heating, superheatedsteam, or a high-temperature gas.
 22. The metal casting apparatus asdescribed in any one of claims 2 to 21, wherein a plurality of heatingsections and a plurality of cooling sections are provided within thecooling member, and functions of respective sections are controlled. 23.The metal casting apparatus as described in any one of claims 2 to 22,further comprising a mechanism for opening at least a portion of thecooling member in the course of solidification of molten metal within amold and a mechanism for supplying a cooling medium directly to anexposed outer surface of a cast ingot.
 24. A cast ingot produced bycharging molten metal into a closed-space-definable mold which includesa cooling member and in which an end surface of an open/close plugserves as a portion of an inner wall of the mold, effecting a localcontrol in terms of removal of heat from a mold member in accordancewith the shape of cast ingot and the location and number of the moltenmetal inlet(s), causing the molten metal to solidify in such a mannerthat the solidification interface advances to arrive at an end of aninner surface of the mold, to thereby provide a cast ingot having no cutsurface or riser portion.